The present invention relates to a battery apparatus for controlling plural high energy battery cells connected in series and its control method, and more particularly to a battery apparatus which is suitable for a low order control devise which controls a battery module having plural battery cells connected in series and a high order control device for giving instructions to plural low order control devices.
For example, Japanese Patent Laid-Open Publication No. 10-322925 describes a conventional battery apparatus which is comprised of plural battery cells connected in series as a battery module, plural battery modules being connected in series, and a low order control device disposed for each battery module, a command being sent from a high order control device to the low order control device. The low order control devices monitor the states of the battery cells possessed by the corresponding battery modules. The low order control devices disposed in the same quantity as that of the battery modules are electrically connected in series via the battery modules, a signal is transmitted between the high order control device and the low order control devices and between the low order control devices by an isolating unit such as a photocoupler in a configuration that no affect is caused by a potential difference between the control devices.
The low order control device adjusts the capacity of the battery cells as described in Japanese Patent Laid-Open Publication No. 2000-92732 for example. The capacity adjustment means the reduction of a voltage difference between the battery cells by having a resistor connected in parallel to the battery cells via a switch, and when the battery cells measured by a voltage detection circuit have a high voltage, driving the switch to partly discharge the amount of electricity stored. Particularly, a lithium-ion battery, which has amorphous carbon with high relevancy between an open-circuit voltage and a remaining capacity as an anode active material, can effectively equalize the capacity of each battery cell by reducing a voltage difference between the battery cells.
In recent years, there has been used an ultra capacitor which can store the same amount of electricity as the secondary battery and has less degradation in service life as compared with the secondary battery. The ultra capacity adopts a method of equalizing the voltage between the capacitor cells as described in Japanese Patent Laid-Open Publication No. 2001-37077 for example. This method provides a circuit which connects a switch in parallel to the capacitor cells to detect the voltage of the capacitor and bypasses part of electricity to the switch. It is similar to the aforesaid Japanese Patent Laid-Open Publication No. 2000-92732.
The low order control device detects a voltage of the battery cell or the capacitor cell, and when the voltage is high, operates the switch to adjust the capacity. Meanwhile, the high order control device sends an instruction signal to make the low order control device to adjust the capacity. In Japanese Patent Laid-Open Publication No. 2000-92732, an open-circuit voltage of each battery cell of the battery module is measured when the low order control device is activated, and the measured value is transmitted to the high order control device. The high order control device calculates a reference voltage value at the time of capacity adjustment from the value of open-circuit voltage obtained from all the low order control devices and gives instructions to the low order control devices again.